Shrink tunnel control apparatus and method

ABSTRACT

Control system and apparatus for controlling power consumption of a heat chamber such as a shrink tunnel. The system and apparatus of the present invention is modification to conventional systems, and takes advantage of the inherent equipment usage model in a packaging process. When the shrink wrap sealer has been idle for a predetermined duration, control circuitry in the shrink tunnel forces the tunnel to enter an energy savings mode.

[0001] This application is a divisional of co-pending Ser. No.10/286,243 filed Nov. 1, 2002, the disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] Packaging systems typically utilize two distinct machines toperform seal and shrink functions. The first is a shrink wrap sealer,which is employed to wrap and seal plastic film about an article. Thesemachines conventionally utilize a heated wire to seal film layers to oneanother and to melt through the layers in order to separate one articlefrom another as the articles pass through the machine. When the sealerjaw is lowered, current is supplied to the wire to heat the wire to ahigh temperature in order to affect the seal and cutting operation. Theappearance of the resulting seal is fine and neat as the film shrinkstightly around the package, especially where polypropylene films areinvolved. Such hot wires are typically used to form both end seals andside seals.

[0003] After the plastic has been wrapped and sealed around the article,the article is transferred into the second machine, a shrink tunnel. Theshrink tunnel is a heated chamber through which the article is passed,typically on a conveyor belt. The heat within the chamber causes theplastic wrap to shrink, tightening it around the article. Tunneltemperature and dwell time are typically variable in order to achievethe desired result for a particular plastic.

[0004] The shrink tunnel uses a large amount of energy to maintain thetunnel at the desired temperature, even in the absence of articlespassing through it, as it runs independently of the sealer. Moreover,heat is lost to the surroundings through both the inlet and the outletof the shrink tunnel, and to the conveyor itself which is often made ofa thermally conductive material.

[0005] In a typical packaging process, articles are passed into theshrink tunnel immediately after they are sealed. It would be desirableto implement an energy saving mode for the shrink tunnel that respondsto inactivity of the shrink wrap sealer in order to reduce the overallpower consumption of the shrink tunnel.

SUMMARY OF THE INVENTION

[0006] The energy consumption problems of the prior art have beenovercome by the present invention, which provides a control system andapparatus for adjusting the energy usage of a heat tunnel, such as ashrink tunnel. The system and apparatus of the present invention is amodification to conventional systems, and takes advantage of theinherent machine usage model of the shrink wrap process. When the shrinkwrap sealer machine, which typically carries out the preceding operationin a packaging process and is generally physically separate from theheat tunnel, has been idle for a predetermined amount of time, the powerconsumption of the shrink tunnel is automatically reduces by entering anenergy efficient mode. In this energy efficient mode, the energy used bycertain high power components of the tunnel, such as the heaters andblower, is reduced, and conveyor speed can be reduced.

[0007] The control system of the present invention thus directlymonitors the activity at the shrink wrap sealer. If the control systemof the shrink tunnel does not detect any sealer activity within apredetermined time period, it forces the shrink tunnel to enter anenergy efficient state, where the temperature, blower speed and/orconveyor speed are reduced to a predetermined percentage of theoperating levels. The aforementioned predetermined time period andpredetermined percentage are preferably user-selectable variables.

[0008] In a preferred embodiment, a wireless signal is generated by theshrink wrap sealer each time the sealer jaw is depressed. Wirelessreceptors at the shrink tunnel receive these signals and pass thisinformation to the control circuitry of the shrink tunnel. This controlcircuitry monitors the elapsed time between these received signals. Ifthe elapsed time between received signals exceeds a duration specifiedby the operator, the control circuitry then enters a power savings mode.

BRIEF DESCRIPTION OF THE DRAWING

[0009]FIG. 1 is a perspective view of a shrink wrap sealer in accordancewith the present invention;

[0010]FIG. 2 is a side view of a shrink wrap sealer in accordance withthe present invention;

[0011]FIG. 3 is a side view of a shrink tunnel in accordance with thepresent invention;

[0012]FIG. 3A is a perspective view of the tunnel of FIG. 3;

[0013]FIG. 4 is a front view of the shrink tunnel user interface; and

[0014]FIG. 5 is a flow chart of the shrink tunnel control electronics inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The typical packaging process includes wrapping a plastic filmaround an article and sealing this film so that it completely envelopsthe article. The film is then made to contract about the article,typically upon the application of heat. This contraction draws the filmtoward the article, causing the article to be tightly wrapped in theplastic film. A shrink wrap sealer performs the wrapping and sealingfunction, while a shrink tunnel heats the plastic to create the tightfit, known as “shrink wrap”.

[0016] Turning now to the figures, there is partially shown theequipment used in a typical packaging process. It should be understoodthat the sealer and tunnel are shown by way of illustration, as thepresent invention is not limited to any particular embodiment of thesealer or the tunnel.

[0017] Referring to FIG. 1, shrink wrap sealer 10 positions the plasticfilm with which the article is to be wrapped. The film is placed aroundthe article, and then sealed. The sealing operation is performed bysandwiching the film between top sealer jaw 11 and bottom sealing jaw11A, the top sealing jaw 11 being pivotally connected to the top surfaceof the shrink wrap sealer 10. The sealer jaw 11 contains a wire or otherelectrical resistance heating element (such as a blade, not shown) thatis heated each time that the jaw is depressed. The heating of this heatsealing element melts together layers of the plastic film to create anenvelope of plastic film around the article.

[0018] In a preferred embodiment, activity of the sealer is indicated bya signal generated when the top seal jaw contacts the bottom seal jaw.For example, mounted on sealer jaw 11 is a jaw magnet 12 (FIG. 2). Uponclosure of the sealer jaw, jaw magnet 12 contacts opposite base magnetswitch 13 on the bottom jaw. This contact generates a signal, which isthen sent to the control circuitry contained in the sealer. The controlcircuitry receives this signal from the magnetic switch, and generatesanother electrical signal that is sent to transmitters as discussedbelow. Other means for generating a signal based upon contact betweenthe top and bottom jaws, such as a momentary switch, could be used andare within the scope of the present invention.

[0019] Referring to FIG. 2, one or more transmitters 13 a and 13 b aremounted on the sealer 10, such as along the side of the sealer leg 14.These transmitters generate a signal each time the sealer jaw 12 isdepressed. In the preferred embodiment, this signal is generatedwirelessly using infrared light. However, those skilled in the art willappreciate that other methods of communication could be used as well.These methods could include other types of optical signals, radio waves,or more traditional cabled connections. Preferably multiple transmittersare used to maximize the field which is covered by the generatedsignals. In the case of infrared light, which is an optical medium,there must be a clear line of sight from the transmitter to thereceiver. This combination of multiple transmitters allows flexibilityin placing the shrink wrap sealer 10 in a variety of positions relativeto the shrink tunnel.

[0020] Referring to FIGS. 3 and 3A, a detector 15 such as an infrareddetector is located on the side of the shrink tunnel 20. This detector15 receives the infrared signal (or other type of signal) sent by thetransmitters 13 mounted on the sealer.

[0021] The shrink tunnel 20 includes a conveyor belt 16 onto which thesealed article is placed. The conveyor belt 16 draws the article beingsealed into the heated compartment 17. Inside the heated compartment 17,there are one or more conventional heating elements (not shown) that areused to raise the temperature of the compartment to a predeterminedlevel. The operator, using the keypad, can select the desiredtemperature of the chamber. Higher temperatures are typically needed forthicker films. The hot air is circulated inside the compartment by ablower fan (not shown). This blower fan insures that the air throughoutthe entire chamber is at a uniform temperature. Articles are transferredinto the tunnel on conveyor belt 16. The speed of the conveyor beltdetermines the amount of time that the article is subjected to thetunnel temperature and is selectable by the operator of the tunnel usingthe keypad.

[0022] The detector 15 is in electrical communication with the shrinktunnel control circuitry via a cable or the like. Each time a signal isdetected by the detector 15, a signal is generated by the detector andsent to the control circuitry. The control circuitry then uses thissignal to determine the proper operation of the shrink tunnel. There aretwo parameters that can be set, such as manually, by the operator tocontrol the power savings mode operation. The first parameter is“Inactivity Time”. This is the amount of time, in minutes, which thesealer jaw must be inactive before the shrink tunnel can enter its powersavings mode. The second parameter is “Power Savings Percentage”. Thisvalue represents the reduction in power, as measured by percentage inblower speed, conveyor belt speed and oven temperature, to beimplemented in the power savings mode.

[0023]FIG. 4 shows the user interface for the shrink tunnel controlcircuitry. It should be understood that the user interface is shown byway of illustration, as the present invention is not limited to anyparticular embodiment of a user interface. This interface allows theoperator to set the two aforementioned parameters. The user interactswith the interface using panel 100. Panel 100 has several buttons, aswell as a display. Power Save button 110 is used to manually initiatethe power savings mode for the shrink tunnel. In other scenarios, it isused to input various power savings parameters. Up button 111 and Downbutton 112 are used to increase and decrease, respectively, the valuesshown on output display 113. This output display is used to inform theuser of various settings, such as oven temperature.

[0024] To set the Inactivity Time, the following steps are taken. Theoperator actuates and holds the Power Save button 110 for apredetermined duration, such as 3 seconds. After this duration, theoutput display 113 will show the current Inactivity Time. This value canbe adjusted, in specific intervals (such as 1-minute intervals), usingUp button 111 and Down button 112. An exemplary minimum value is 5minutes, while an exemplary maximum Inactivity Time value is 255minutes. In this embodiment, an Inactivity Time value of 0 willcompletely disable the power savings mode and neither the Power Savebutton 110 nor the lack of sealer activity will allow the tunnel toenter Power Savings mode. An Inactivity Time value of 255 has the effectof setting an infinite Inactivity Time. In this case, lack of sealeractivity will never cause the shrink tunnel to enter Power Savings mode.However, Power Savings mode can still be invoked, such as by actuatingPower Save button 110. Because of the special operations associated withvalues of 0 and 255, the useful range of the Inactivity Time is from 5minutes up to 250 minutes. Those skilled in the art will appreciate thatthe upper value of 255 is chosen by way of illustration; other valuescan be chosen to achieve the same objective.

[0025] After the operator has input the desired Inactivity Time value,he may actuate the Power Save button 110 again in order to set the PowerSavings Percentage. If the Power Save button 110 is actuated while theoutput display 113 is still showing the Inactivity Time value, thecontrol circuitry will then display the current Power SavingsPercentage. This value can be adjusted using the Up button 111 and theDown button 112 in a manner similar to that used for the InactivityTime. The value of the Power Savings Percentage can be from 0 to 99. Inthe current implementation, any value above 95 will cause the shrinktunnel to shut down when Power Savings mode is entered. The PowerSavings Percentage determines the extent of the operation of the shrinktunnel while in Power Savings mode.

[0026] As an illustration of the power savings mode, a tunnel with a300° operating temperature and a Power Savings Percentage of 40% wouldreduce its temperature to 120° and reduce the speed of the blowers andconveyor belts to 40% of their normal operating rates in Power Savingsmode.

[0027]FIG. 5 is a flowchart illustrating the process used to determinewhether to enter Power Savings mode. Decision Box 200 checks whether thesealer jaw is closed. If the jaw is closed, as determined by thepresence of a signal at the infrared detectors, the code progresses toAction Box 201. In this Box, a flag, called Jaw Active, is set. The JawActive flag is used to denote that the jaw has been activated at leastone time before Power Savings mode is invoked. Additionally, the jawtimer, which counts the minutes since the last sealer jaw operation, isreset. This path is followed each time the sealer jaw closes.

[0028] If the jaw is not closed, the code progresses to Decision Box202. If the jaw timer has not been set, this means that either thesealer jaw has never closed, or it was closed the previous time thatthis code was executed. Decision Box 203 determines whether the sealerjaw has ever been closed by checking the Jaw Active flag that only getsset in Action Box 201. If the Jaw Active flag is not set, the sealer jawhas not been used and the code terminates. This behavior guarantees thatthe shrink tunnel will never enter power savings mode unless the sealerjaw has closed at least once.

[0029] Action Box 205 is executed if the sealer jaw has just opened. Inthis case, the Jaw Active flag will be set, but the Jaw timer has notbeen set to the Inactivity Time. Action Box 205 sets the Jaw timer tothe Inactivity Time. This timer now begins counting down toward zero.

[0030] Decision Box 204 is entered if the sealer jaw is currently open,but the Jaw timer has been already set. If the timer has not reached theInactive Time, the code simply terminates. If the timer has expired, thesealer jaw has been inactive for at least the amount of time specifiedby the Inactivity Time. If all other conditions are met, the shrinktunnel should enter power savings mode.

[0031] Decision Box 206 checks if automatic power saving mode has beenenabled. If the Inactivity Time was set to 0 or 255, the shrink tunnelwill not enter power savings mode and the code terminates. If theInactivity Time is set to any value between 5 and 250, the code willmove to Decision Box 207.

[0032] Decision Box 207 checks if the tunnel is already in a shutdownprocess. In this embodiment, there is a cool down mode wherein thetunnel is cooled to a lower temperature before being completely turnedoff. If the shrink tunnel is in cool down mode, the code simplyterminates. If the tunnel is operating normally, the code moves toDecision Box 208.

[0033] Decision Box 208 checks if the blowers or conveyor are currentlyrunning. If they are operating normally, all of the conditions necessaryto enter power savings mode have been met, and the control circuitrymodifies the blower and conveyor belt speeds based on the Power SavingsPercentage. The tunnel temperature is also reduced in accordance withthe Power Savings Percentage. It is in this Decision Box that the oven,belt and blowers will all be turned off if the Power Savings Percentageexceeds 95%.

[0034] In the current embodiment, once the shrink tunnel has enteredpower savings mode, it can only resume normal operation by actuation ofthe Power Save button 110. Resumed sealer jaw activity will notautomatically cause the shrink tunnel to resume normal operation. Thisis done to ensure that the operator is aware that the tunnel has entereda reduced power mode and allows the tunnel sufficient time to return toits normal operating temperature before placing more articles on theconveyor mode.

[0035] In another embodiment, the conveyor speed is reduced to 0 whenthe tunnel enters power savings mode. Renewed sealer jaw activityautomatically causes the shrink tunnel to return to normal operation.Since the tunnel needs significant time to return to normal operatingtemperature, the operator cannot place articles in the shrink tunnelimmediately. To insure that articles are not presented to the tunneluntil it is fully operational, the conveyor belt does not turn back onuntil the shrink tunnel has returned to its normal operatingtemperature. Once the conveyor belt resumes operation, it is safe to usethe shrink tunnel.

What is claimed is:
 1. Apparatus for controlling the temperature of a heat chamber, comprising: a shrink wrap sealer machine; a first device responsive to usage of said sealer machine for generating a signal when said sealer is active; a detector for detecting when said signal is generated; and a second device responsive to said detector for reducing power consumption of said heat chamber by a predetermined percentage when the duration between said detected signals exceeds a predetermined threshold.
 2. The apparatus of claim 1, wherein said shrink wrap sealer machine comprises a sealer jaw, and said first device generates said signal when said sealer jaw is depressed.
 3. The apparatus of claim 1, wherein said first device generates said signal wirelessly.
 4. The apparatus of claim 3, wherein there is a plurality of said first devices.
 5. The apparatus of claim 1, wherein said detector is mounted on said heat chamber.
 6. The apparatus of claim 1, wherein said detector detects said signal wirelessly.
 7. The apparatus of claim 1, wherein said second device reduces power consumption of said heat chamber by reducing chamber temperature.
 8. The apparatus of claim 1, wherein said heat chamber comprises at least one blower, and said second device reduces power consumption of said heat chamber by reducing the speed of said at least one blower.
 9. The apparatus of claim 1, wherein said heat chamber comprises a conveyor belt, and said second device reduces power consumption of said heat chamber by reducing the speed of said conveyor belt.
 10. The apparatus of claim 1, wherein said predetermined percentage is manually selectable.
 11. The apparatus of claim 1, wherein said predetermined threshold is manually selectable.
 12. Control system for minimizing power consumption of one of first and second associated film packaging machine components for packaging an article, wherein said first packaging machine component comprises upper and lower sealing jaws for sealing therebetween said film about said article, at least one of said upper and lower sealing jaws being movable with respect to the other between an open position and a closed position, said closed position causing the generation of a signal indicative of said position; said second packaging machine component comprising a heated cavity for receiving the packaged article, said heated cavity requiring an amount of power to generate sufficient heat to shrink said film about said article; said control system comprising a receiver for receiving said generated signal and a controller for determining the duration between said generated signals received by said receiver and reducing said amount of power when said duration exceeds a predetermined value. 